1. Field of the Invention
The invention relates to a diagnostic device and method for monitoring the operation of control loops of an automation system.
2. Background of the Invention
The maintenance and servicing of automation systems can be improved if subsystems or components are monitored to ensure that they are functioning correctly. In the event of a degradation in operational performance, a targeted intervention can be carried out at the right point in the system by means of servicing, maintenance or troubleshooting measures. Components of automation engineering installations are often interconnected in control loops. To enable, in response to a deterioration in operating efficiency of individual control loops, timely and targeted intervention at the right point in the system through maintenance or controller optimization measures, it would be advantageous to continuously and automatically monitor the control performance of such control loops.
A diagnostic method for monitoring the operation of a control loop is already known from EP 1 528 447 B1. In an essentially stationary state, i.e. given a largely constant setpoint setting, the variance in a sequence of actual-value data is determined as a stochastic signal feature and evaluated to analyze the state of the control loop. In response to an excitation of the control loop corresponding to a step change in setpoint value, the relative overshoot and/or the settling ratio, i.e. the quotient from rise time and settling time of the controlled process variable, are evaluated as deterministic signal features for use in analyzing the state of the control loop.
In chemical processing plants or process control installations that are equipped with automation systems, numerous single-loop control loops, for example comprising PID controllers, are linked with one another in most cases via physical, thermodynamic, chemical or biological interactions of the respective overall process. Any movement in a control loop can therefore have an impact in the nature of a disturbance on other control loops. Since interactions between the control loops, which in this disclosure are also referred to as cross-influences, couplings or interaction effects, do not generally represent a problem in the operation of a system, they are not in most instances more closely scrutinized by plant operators and are not included in the monitoring of control loops operation. If they were taken into account, however, it would be possible in certain circumstances to achieve a significant improvement in the operation of the system, for example with regard to energy efficiency or the quality of the products being produced with the aid of the system.